In order to prevent oxygen oxidation and store various types of articles, represented by foods, beverages, medicinal products, and cosmetics, which easily deteriorate or degrade under the effect of oxygen for a long time, oxygen absorbents are used for removing oxygen within packaging bodies storing these articles.
As the oxygen absorbent, an oxygen absorbent containing an iron powder as a reactive main component is generally used in view of oxygen-absorbing ability, handling and safety. However, the iron-based oxygen absorbent is responsive to a metal detector and thus it is difficult to use a metal detector in inspecting foreign matter. Furthermore, packaging bodies containing an iron-based oxygen absorbent have a risk of ignition, and thus, they cannot be heated by a microwave oven. Moreover, the oxidation reaction of an iron powder requires water, and thus, an oxygen-absorbing effect is exerted only on an article to be packaged rich in moisture content.
Packaging containers are developed by making the container of a multilayer material having an oxygen-absorbing layer formed of an oxygen-absorbing resin composition containing a thermoplastic resin and an iron-based oxygen absorbent, thereby improving a gas barrier property of the container and providing an oxygen-absorbing function to the container itself (see, Patent Literature 1). Specifically, the multilayer material is an oxygen-absorbing multilayer film, which is obtained by providing an oxygen-absorbing layer formed of a thermoplastic resin having an iron-based oxygen absorbent dispersed therein between layers of a gas barrier multilayer film having a conventional structure (in which a heat sealing layer and a gas a barrier layer are laminated), which has a function of absorbing oxygen within the container in addition to a function of preventing oxygen transmission from outside, and which is manufactured using a conventional manufacturing method known in the art, such as extrusion lamination, coextrusion lamination and dry lamination. However, such an oxygen-absorbing multilayer film has the same problems: a metal detector for inspecting foreign matters cannot be used since it responds to the metal detector for inspecting foreign matters in foods etc.; heating cannot be made by a microwave oven; and the effect is only exerted on an article to be packaged rich in moisture content. In addition, the multilayer film has a problem of opacity, leading to insufficient visibility of content.
In addition to these problems, in molding an oxygen-absorbing multilayer sheet using an iron powder, since the sheet itself is heavy due to the presence of the iron powder, imperfect molding occurs during article molding. Examples of problems include neck-in and thickness deviation during sheet molding and draw-down during thermoforming. In addition, an uneven surface may be resulted in molding.
In the aforementioned circumstances, it has been desired to develop an oxygen absorbent containing an organic substance as a reactive main component. As the oxygen absorbent containing an organic substance as a reactive main component, an oxygen absorbent containing ascorbic acid as a main component is known (see, Patent Literature 2).
In the meantime, an oxygen-absorbing resin composition composed of a resin and a transition metal catalyst is known. For example, a resin composition composed of a polyamide as an oxidizable organic component (in particular, a xylylene group-containing polyamide) and a transition metal catalyst, is known (see, Patent Literatures 3 and 4). In Patent Literatures 3 and 4, articles obtained by molding such a resin composition, such as an oxygen absorbent, a packaging material and a multilayer laminated film for packaging are further exemplified.
As an oxygen-absorbing resin composition requiring no moisture content for absorbing oxygen, an oxygen-absorbing resin composition composed of a resin having a carbon-carbon unsaturated bond and a transition metal catalyst, is known (see, Patent Literature 5).
As a composition for trapping oxygen, a composition composed of a polymer containing a substituted cyclohexene functional group or a low molecular-weight substance bound with the cyclohexene functional group and a transition metal is known (see, Patent Literature 6).
A tubular container is used for storing a wide variety of articles including foods, medicinal products, cosmetics, hygiene products such as toothpastes and chemical products such as adhesives. There are many structures of materials for forming the containers, shapes of the containers and manufacturing methods thereof known in the art. As these tubular containers, containers using an aluminum-foil as a gas barrier layer, which is laminated with other layer(s), have long been used to prevent deterioration of contents, particularly deterioration by oxygen. The aluminum foil is excellent as a material that can completely block transmission of a gas such as oxygen and has been used as a container, particularly for medicinal products etc.
However, in a tubular container using an aluminum-foil laminate, it is extremely difficult to separate a laminated resin from aluminum foil and collect them separately for recycling after use. In discarding it by incineration, aluminum foil produces an ash-like residue. Disposal of waste becomes difficult due to the ash-like residue. As a means for solving such a problem, many proposals have been made, in forming a tubular container, to replace aluminum foil with a thermoplastic resin excellent in gas barrier property, such as an ethylene-vinyl alcohol copolymer and a polyamide (hereinafter, sometimes referred to as “nylon MXD6”) obtained from metaxylylenediamine and adipic acid, or with a resin film, which is formed by vapor deposition of an inorganic oxide such as aluminum oxide and silicon oxide, and such containers have been put into practical use.
In the meantime, in the cases of containers filled with drug solutions such as medicinal products, an oxygen absorbent is used for removing oxygen within the packaging bodies containing these containers in order to prevent oxygen oxidation of the drug solutions, which easily deteriorate and degrade upon the effect of oxygen, in the containers and store them for a long time.
The container filled with a drug solution is packed in an outer package formed of a synthetic resin film in order to prevent contamination of the container until actually put in use and the container is handled while being packed in the outer package. Since the container is made of an oxygen transmissible resin in view of sanitation etc., the outer package needs to have a gas barrier property in order to prevent deterioration of the content fluid due to oxygen. However, oxygen is more or less present in the outer package even if package is sealed, and oxygen transmits with the passage of time even if the gas-barrier outer package is used. Thus, it is necessary to prevent deterioration of the content fluid caused by such oxygen. Then, up to now, a container filled with a drug solution is not only stored at a low oxygen concentration, but also placed in an outer package together with an oxygen absorbent. Since residual oxygen in the outer package as well as oxygen transmitted from outside are absorbed by the oxygen absorbent, the amount of oxygen within the outer package can be maintained at a low level to prevent the deterioration of the content fluid in an infusion container.
As anti-inflammatory agents for joint pain, muscular pain, etc., patches containing various types of medicinal ingredients are hermetically packaged and stored by use of a film having a barrier property.
When patches containing medicinal ingredients are stored, in order to prevent deterioration of the medicinal ingredients by oxygen, it is necessary for the film to be used in hermetic packaging to have a gas barrier property. However, since oxygen remains within the packaging body after hermetical closing and a small amount of oxygen transmits even if the packaging body has a gas barrier property, such oxygen must be removed in order to suppress deterioration of medicinal ingredients. Up to present, patches have been hermetically packed together with an oxygen absorbent or in a packaging bag having an oxygen-absorbing function.
In the meantime, in the field of packaging medicinal products and foods, etc., containers and packaging bodies such as PTP packaging body (press-through package, also called a blister package) are widely used for packaging medicinal agents such as tablets and capsules, particulate foods, etc. The PTP packaging body refers to a packaging body using a plastic sheet of, e.g., a polyvinyl chloride resin and a polypropylene resin as a bottom material and having a pocket portion for containing an article to be packaged, which is formed by applying air-pressure forming, vacuum molding, etc. After an article to be packaged is contained in the pocket portion, the pocket portion is sealed by laminating a foil or a film made of a material that can be easily torn or easily opened by hand, such as aluminum foil serving as a cover material. In the PTP packaging body, if a transparent plastic sheet is used as a bottom material, an article to be packaged contained in the pocket portion can be directly observed by the naked eye before opening it. In opening the packaging body, the cover material is broken by pressing a perverse from the pocket portion side by a finger. In this way, an article to be packaged can easily be taken out.
As a method for storing fruit pulps such as mandarin orange, chestnut, cherry, peach, apple and pineapple, a technique for storing them in a metal can like canned food is known. As a method for storing alcohol beverages such as Japanese sake, wine and shochu and liquid-state tea or paste-state tea, a technique for storing them in metal cans and glass bottles is known. Recently, fruit juices and/or vegetable juices obtained by processing various types of fruits and/or vegetables have been developed. If these fruit juices and/or vegetable juices are exposed to oxygen, their components such as flavor components, sugars and vitamins are oxidatively decomposed and cause degradation, with the result that the juices change in color tone and lose taste and flavor. Then, a technique for storing fruit juices and/or vegetable juices in metal cans and glass bottles is conceived, in the same manner as in alcohol beverages. However, metal cans and glass bottles have a problem of non-combustible waste treatment and are required to reduce weight. In addition, metal cans have a problem in that metal components leak out into a content. Because of this, metal cans and glass bottles have been replaced with plastic containers such as a gas barrier bag and a gas barrier tray.
In dry products such as coffees, teas, peanuts, lavers, fish clause powders, seasonings and dried vegetables, whose taste and flavor and color tone determine commodity values, it is important to keep taste and flavor and color tone in maintaining commodity value and product life for a long time. Degradation of dry products and reduction of characteristic taste and flavor of dry products during distribution and storage period of products are mainly caused by oxygen present in their packaging containers.
In addition, as medical packaging containers for packaging and storing a drug solution in a hermetically closed condition, glass ampoules, vials, prefilled syringes, etc. have been conventionally used. However, these glass containers have problems: sodium ion etc. elute off from the container to a liquid content stored therein; and micro substances called flakes generate; when a light-blocking glass container colored with a metal is used, the content is contaminated with the coloring metal; and the container is easily broken by drop impact. In addition to these problems, since glass containers have a relatively large specific gravity, medical packaging containers become heavy. For these reasons, development of alternate materials has been desired. To be more specific, materials lighter than glass, such as a polyester, a polycarbonate, a polypropylene and a cycloolefin polymer, have been investigated as glass alternatives.
For example, a medical container formed of a polyester resin material is proposed (see, Patent Literature 7).
In the meantime, a multilayer container having a gas barrier layer as an intermediate layer in order to provide a gas barrier property to a container made of plastic, has been investigated. Specifically, a prefilled syringe improved in oxygen barrier property by constituting the innermost layer and the outermost layer formed of a polyolefin resin and an intermediate layer formed of a resin composition excellent in oxygen barrier property is proposed (see, Patent Literature 8). Other than this, multilayer containers obtained by laminating a gas barrier layer formed of e.g., a polyamide, which is obtained from metaxylylenediamine and adipic acid, an ethylene-vinyl alcohol copolymer, a polyacrylonitrile, a poly(vinylidene chloride), an aluminum foil, a carbon coat or a vapor-deposited inorganic oxide, on a resin layer, have been investigated.
In recent years, it has been proposed that a small amount of transition metal compound is added to nylon MXD6 and mixed to provide an oxygen-absorbing function and the resultant material is used as an oxygen barrier material constituting containers and packaging materials (see, Patent Literature 9).
Examples of the medical containers include ampoules, vials and syringes. Other than these, examples of the medical containers include an artificial kidney hemodialyzer (dialyzer). As a housing of a dialyzer, a polystyrene and a polycarbonate are used as a transparent (easy to see the content) plastic. Of them, a polycarbonate having satisfactory impact resistance is more favorably used in order to avoid breakage by impact of dropping or other causes (see Patent Literature 10).